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Wafer as Feed Supplement Stimulates the Productivity of Bali Calves
Available online at www.sciencedirect.com
ScienceDirect APCBEE Procedia 8 (2014) 173 – 177
2013 4th International Conference on Agriculture and Animal Science (CAAS 2013) 2013 3rd International Conference on Asia Agriculture and Animal (ICAAA 2013)
Wafer as Feed Supplement Stimulates the Productivity of Bali Calves Y. Retnania , C. Armanb, S. Saidc, I.G. Permanaa, A. Saenabd a
Department of Nutrition and Feed Technology, Faculty of Animal Science ,Bogor Agricultural University,Jln Agatis, Kampus IPB. Bogor, 16680. Indonesia b Faculty of Animal Science, Mataram University, Jln Majapahit No.62, Mataram. Indonesia c Indonesian Institute of Sciences,Jln Raya Bogor, Km. 46. Bogor. Indonesia d Department of Agriculture, Jln Raya Ragunan No. 30, Kelurahan Jati Padang, Kecamatan Pasar Minggu, Indonesia
Abstract The aim of this research was to determine the nutrient content, digestibility on wafer of feed supplement and productivity of Bali calves. This research had two steps experimental, the first steps experiment to determine the nutrient content and digestibility on wafer of feed supplement. The composition wafer of feed supplement i.e. T1 = wafer containing lamtoro leaf, T2 = wafer containing lamtoro and papaya leaf, T3 = wafer containing moringa leaf, T4 = wafer containing gamal leaf, T5= wafer containing corn leaf and corn. Nutrient content and digestibility of T1 had highest compared among the others, i.e. crude protein (32.34%), ash (7.24%), crude fiber (16.85%), crude fat (4.52%), NFE (39.06 cal/g), digestibility of dry matter 82.87 %, digestibility of organic matter 81.78%, NH3 9.33% and VFA 164.55%. The second steps of this research was the best result of the nutrient content and digestibility of wafer of feed supplements tested to bali calves. Level of wafer containing lamtoro leaf ,i.e R1 =0%, R2 =5%, R3 =10%, R4=15%. The result indicated that treatments had significant effect (P<0.05) on daily weight gain. It was concluded that bali calves were fed by wafer of feed supplement with level 10% had 69% higher than conventional. © 2014 Retnani. Published by Elsevier B.V. This isand/or an openpeer access article under under the CC BY-NC-ND © 2013Y.Published by Elsevier B.V. Selection review responsibility of license Asia-Pacific (http://creativecommons.org/licenses/by-nc-nd/3.0/). Chemical, Biological & Environmental Engineering Society
Selection and peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society
Keywords:bali calves, digestibility, feed supplement, productivity, wafer
YuliRetnani. Tel.: +62812804451; fax: +621-626877. E-mail address: [email protected]
2212-6708 © 2014 Y. Retnani. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society doi:10.1016/j.apcbee.2014.03.022
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Y. Retnani et al. / APCBEE Procedia 8 (2014) 173 – 177
1. Introduction Strategic issues facing the world today is global climate change, food and energy crisis. Given these conditions many food exporting countries tend to export their products to be used as stock food. The people will choose the better food quality in animal products. Bali cattle have been developed in NTB province. Bali cattle are the result of domestication of bison (bison bibos) natural habitat on the island of Bali. Beef market potential outside the NTB area large enough, demand reached 50.000 head of beef cattle per year. Development of cattle farms is not enough just to increase the population with the government's efforts to provide assistance cattle or business capital. The application of technology has to be initiated in order to obtain production efficiency and production cost efficiency [1]. The major constraints of ruminant feed are as follows: low quality of forage; the level of palatability and digestibility is low. Therefore, it is necessary to develop suitable technologies to produce ruminant feed which is more durable, easier to handle, more convenient to distribute and are available in all seasons [2]. During the rainy season, forage is abundant, but during the dry season forage very little or none so that the local calves can decrease its productivity [3]. To solve this problem is making forage into wafer feed. A pressing technology can make the feed products into a wafer form. The wafer feed must contain energy; mineral; vitamin and protein that are needed by animal to increase productivity [4]. Wafer of feed supplement is made of fiber, especially fresh green forage as a replacement for ruminants in order to utilize the fiber when the quality and quantity of forage decreased [2]. 2. Materials and Methods This research was conducted with 2 steps. The first research of testing the nutrient content and digestibility of wafer of feed supplement. Wafer of feed supplement was tested for nutrient content and digestibility are wafer containing lamtoro leaf (T1), wafer containing lamtoro and papaya leaf (T2), wafer containing moringa leaf (T3), wafer containing gamal leaf (T4), wafer containing corn leaf and corn (T5). The second steps of this research is the best result of the nutrient content and digestibility of wafer of feed supplements tested to Bali calves. Level feeding wafer of feed supplement i.e. R1 (100% of conventional feed), R2 (5% wafer of feed supplement), R3 (10% wafer of feed supplement), R4 (15% wafer of feed supplement). The research used 12 heads of Bali calves with the average initial body weight around 105.17 ± 22.68 kg. The experimental Bali calves was maintained individually. The process of wafer of feed supplement production was conducted by chopping, drying, mixing, preassing, heating and forming with temperature of 1000C for 10 minutes to get wafer of feedsupplement and then being cooled in room temperature. 2.1. Experimental Design of the Second Research The experimental design of the second steps used in this research was a randomized block design with four treatments and three replications. The treatments were wafer of feed supplement production composition i.e : R1 (100% of conventional feed), R2 (5% wafer of feed supplement), R3 (10% wafer of feed supplement), R4 (15% wafer of feed supplement). Conventional feed is field grass. The data was analyzed with the analysis of variance, and the differences among treatments were examined with orthogonal contrast [5].The parameters measured were productivity of Bali calves , i.e. daily weight gain and body weight.The variables that would be measured were:
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Daily weight gain was calculated by: Daily weight gain (g/head/day) =Final body weight gain (g) – initial body weight gain (g) During the research (days) Body weight was calculated by weighing the cattle body weight every 1 weeks during the maintenance 3. Results and Discussion Physical form of wafer of feed supplement was a cube with the size of 5x5x5 cm3. The texture ofwafer feed wasrough with the size of coarse particle. The nutrient content of wafer of feed supplement (% Dry Mater) are presented on Table 1. Table 1. Nutrient Content of Wafer of Feed Supplement (% Dry Mater) Wafer of Feed Supplement
Ash (%)
Crude protein (%)
Crude Fiber (%)
Crude fat (%)
NFE (cal/gr)
T1
7.24
32.34
16.85
4.52
39.06
T2
7.91
29.85
16.52
4.69
41.14
T3
6.24
31.24
14.98
3.89
43.64
T4
6.12
31.48
15.26
3.56
43.58
T5
6.49
31.19
17.27
3.63
41.41
Wafer containing lamtoro leaf (T1), wafer containing lamtoro and papaya leaf (T2), wafer containing moringa leaf (T3), wafer containing gamal leaf (T4), wafer containing corn leaf and corn (T5). Wafer of feed supplement hada highcrude protein content. The average crude protein content of wafer of feed supplement was around 29.85-32.34%. Wafer containing lamtoro leaf had the best crude protein content (T1) of 32,34%. Digestibility test on wafer of feed supplement are presented on Table 2. Table 2. Digestibility of Wafer of Feed Supplement Perlakuan
Organicmatter digestibility (%)
T1
Dry matter digestibility (% ) 82.87 ±1.04
NH3
VFA
81.78 ±0.97
9.33 ±0.34
164.55 ±0.00
T2
81.70 ±1.13
81.33 ±1.22
7,63 ±0,00
140.55 ±0.00
T3
76.71 ±1.88
75.67 ±2.57
5,24 ±0,16
102.93 ±16.17
T4
79.36 ± 1.47
78.76±2.47
6,44 ±0,17
126.59 ±16.27
T5
80.41 ±0.19
80.03 ±0.22
7,19 ±0,16
123.29 ±15.85
Wafer containinglamtoro leaf (T1), wafer containing lamtoro and papaya leaf (T2), wafer containing moringa leaf (T3), wafer containing gamal leaf (T4), wafer containing corn leaf and corn (T5). Wafer containinglamtoro leaf had the best digestibility i.e dry matter digestibility of 82.87%, organic matter digestibility of 81.78%, 9.33 NH3 and 164.55 VFA. The results of the first steps research showed that wafer containing lamtoro leaf has the higest nutrient content and digestibility.
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The second step of the research was feeding by wafer containing lamtoro leaf to stimulate the productivity of Bali calves. The result showed that wafer feeding treatment was significant (P<0.05) on daily weight gain of Bali calves. The feeding treatment did not have significant effect (P>0.05) in blocking the daily weight gain. It means that, wafer of feed supplement given to Bali calves that had the small, medium and big weight had the same response to the wafer of feed supplement. The daily weight gain of Bali calves are presented on Table 3. Table 3. Daily Weight Gain of Bali calves by feeding wafer of feed Supplement (g/head/day) Treatment
Block
Average
B1
B2
B3
R1
33.33
116.67
200.00
R2
50.00
216.67
233.33
R3
350.00
433.33
350.00
116.67 ± 83.33a 166.67 ± 101.38b 377.78 ± 48.11c
c R4 316.67 366.67 450.00 377.78 ± 67.36 R1 (100% of conventional feed), R2 (5% wafer of feed supplement), R3 (10% wafer of feed supplement), R4 (15% wafer of feed supplement). B1 (Small body weight block), B2 (medium body weight block), B3 (Big body weight)
Feeding of 10% and 15% wafer of feed supplement had thesamedaily weight gain (377.78 g/head/day). It suggested that feeding of 10% wafer of feed supplement is optimal. The dailyweight gainin this study is ranged from166.67-377.78g/head/day. The treatments of R3 and R4(10% and 15% of wafer of feed supplement)were higher daily weigth gain thanother treatments. The daily weight gain Bali calves was about 310 g/head/day [6]. According to NRC[7],the daily weight gain was influenced by several factors, i.e. the total consumption of protein, sex, age, genetic, environmental, physiological condition of livestock and management. The result showed thatwafer containing lamtoro leaf treatment was not significant (P>0.05) on body weight of Bali calves during 4 weeks treatment and also did not have significant effect(P>0.05) in blocking body weight of Bali calves. Fig. 1 shows that the average body weight of Bali calves fed by 15% of feed wafer of feed containing lamtoro had the higher average body weight per weeks highest than the other treatment. The Bali calves had the high the responds to the wafer containing lamtoro leaf.
Fig. 1. The Average Body Weight of TheBali Calves.
4. Conclusion It was concluded that bali calves were fed by wafer of feed supplement with level 10% had 69% higher
Y. Retnani et al. / APCBEE Procedia 8 (2014) 173 – 177
than conventional.
References [1] Sasongko WR, Farida SM. Scrutinize Cattle Trade Situation in NTB. BPTP Nusa Tenggara Barat 2012;(http://ntb.litbang.deptan.go.id/ind/index.php?option=com_content&view=article&id=761:menyimak-situasi-perdagangan-sapi-dintb&catid=53:artikel&Itemid=49). [2] Retnani Y, Idat GP, Lia CP. Physical Characteristic and Palatability of Biscuit-Biosupplement For Dairy Goat. Pakistan Journal Of Biological Sciences 2013a; p: 1-5. [3] Retnani Y, Andi S, Taryati. Vegetable Waste as Wafer Feed For Increasing Productivity of Sheep. Asian Jurnal of Animal Sciences 2013b; p: 1-5 [4] Retnani, Y., F.P. Syananta, L. Herawati, W. Widiarti and A. Saenab. Physical Characteristic and Palatability of Market Vegetable Waste Wafer for Sheep. Journal Animal Production 2010a; 12; p. 29 -33. [5] Steel RGD, JH. Torrie. Principles and Procedures of Statistic, 2nd ed. Graw-Hall, Book Comp, New York; 1993. [6] Batubara A, Agussalim..Bioplus effect of bali Cattle. Library of Departement Agriculture 2000; (http://www.pustaka.litbang.deptan.go.id/bptpi/lengkap/IPTANA/fullteks/BPTPsumut/2006B1/pros67.pdf); p:496-501. [7] NRC. Nutrient Requirement of Sheep. 6th Edn. National Academy Press. Washington DC; 1985
177
ScienceDirect APCBEE Procedia 8 (2014) 173 – 177
2013 4th International Conference on Agriculture and Animal Science (CAAS 2013) 2013 3rd International Conference on Asia Agriculture and Animal (ICAAA 2013)
Wafer as Feed Supplement Stimulates the Productivity of Bali Calves Y. Retnania , C. Armanb, S. Saidc, I.G. Permanaa, A. Saenabd a
Department of Nutrition and Feed Technology, Faculty of Animal Science ,Bogor Agricultural University,Jln Agatis, Kampus IPB. Bogor, 16680. Indonesia b Faculty of Animal Science, Mataram University, Jln Majapahit No.62, Mataram. Indonesia c Indonesian Institute of Sciences,Jln Raya Bogor, Km. 46. Bogor. Indonesia d Department of Agriculture, Jln Raya Ragunan No. 30, Kelurahan Jati Padang, Kecamatan Pasar Minggu, Indonesia
Abstract The aim of this research was to determine the nutrient content, digestibility on wafer of feed supplement and productivity of Bali calves. This research had two steps experimental, the first steps experiment to determine the nutrient content and digestibility on wafer of feed supplement. The composition wafer of feed supplement i.e. T1 = wafer containing lamtoro leaf, T2 = wafer containing lamtoro and papaya leaf, T3 = wafer containing moringa leaf, T4 = wafer containing gamal leaf, T5= wafer containing corn leaf and corn. Nutrient content and digestibility of T1 had highest compared among the others, i.e. crude protein (32.34%), ash (7.24%), crude fiber (16.85%), crude fat (4.52%), NFE (39.06 cal/g), digestibility of dry matter 82.87 %, digestibility of organic matter 81.78%, NH3 9.33% and VFA 164.55%. The second steps of this research was the best result of the nutrient content and digestibility of wafer of feed supplements tested to bali calves. Level of wafer containing lamtoro leaf ,i.e R1 =0%, R2 =5%, R3 =10%, R4=15%. The result indicated that treatments had significant effect (P<0.05) on daily weight gain. It was concluded that bali calves were fed by wafer of feed supplement with level 10% had 69% higher than conventional. © 2014 Retnani. Published by Elsevier B.V. This isand/or an openpeer access article under under the CC BY-NC-ND © 2013Y.Published by Elsevier B.V. Selection review responsibility of license Asia-Pacific (http://creativecommons.org/licenses/by-nc-nd/3.0/). Chemical, Biological & Environmental Engineering Society
Selection and peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society
Keywords:bali calves, digestibility, feed supplement, productivity, wafer
YuliRetnani. Tel.: +62812804451; fax: +621-626877. E-mail address: [email protected]
2212-6708 © 2014 Y. Retnani. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society doi:10.1016/j.apcbee.2014.03.022
174
Y. Retnani et al. / APCBEE Procedia 8 (2014) 173 – 177
1. Introduction Strategic issues facing the world today is global climate change, food and energy crisis. Given these conditions many food exporting countries tend to export their products to be used as stock food. The people will choose the better food quality in animal products. Bali cattle have been developed in NTB province. Bali cattle are the result of domestication of bison (bison bibos) natural habitat on the island of Bali. Beef market potential outside the NTB area large enough, demand reached 50.000 head of beef cattle per year. Development of cattle farms is not enough just to increase the population with the government's efforts to provide assistance cattle or business capital. The application of technology has to be initiated in order to obtain production efficiency and production cost efficiency [1]. The major constraints of ruminant feed are as follows: low quality of forage; the level of palatability and digestibility is low. Therefore, it is necessary to develop suitable technologies to produce ruminant feed which is more durable, easier to handle, more convenient to distribute and are available in all seasons [2]. During the rainy season, forage is abundant, but during the dry season forage very little or none so that the local calves can decrease its productivity [3]. To solve this problem is making forage into wafer feed. A pressing technology can make the feed products into a wafer form. The wafer feed must contain energy; mineral; vitamin and protein that are needed by animal to increase productivity [4]. Wafer of feed supplement is made of fiber, especially fresh green forage as a replacement for ruminants in order to utilize the fiber when the quality and quantity of forage decreased [2]. 2. Materials and Methods This research was conducted with 2 steps. The first research of testing the nutrient content and digestibility of wafer of feed supplement. Wafer of feed supplement was tested for nutrient content and digestibility are wafer containing lamtoro leaf (T1), wafer containing lamtoro and papaya leaf (T2), wafer containing moringa leaf (T3), wafer containing gamal leaf (T4), wafer containing corn leaf and corn (T5). The second steps of this research is the best result of the nutrient content and digestibility of wafer of feed supplements tested to Bali calves. Level feeding wafer of feed supplement i.e. R1 (100% of conventional feed), R2 (5% wafer of feed supplement), R3 (10% wafer of feed supplement), R4 (15% wafer of feed supplement). The research used 12 heads of Bali calves with the average initial body weight around 105.17 ± 22.68 kg. The experimental Bali calves was maintained individually. The process of wafer of feed supplement production was conducted by chopping, drying, mixing, preassing, heating and forming with temperature of 1000C for 10 minutes to get wafer of feedsupplement and then being cooled in room temperature. 2.1. Experimental Design of the Second Research The experimental design of the second steps used in this research was a randomized block design with four treatments and three replications. The treatments were wafer of feed supplement production composition i.e : R1 (100% of conventional feed), R2 (5% wafer of feed supplement), R3 (10% wafer of feed supplement), R4 (15% wafer of feed supplement). Conventional feed is field grass. The data was analyzed with the analysis of variance, and the differences among treatments were examined with orthogonal contrast [5].The parameters measured were productivity of Bali calves , i.e. daily weight gain and body weight.The variables that would be measured were:
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Y. Retnani et al. / APCBEE Procedia 8 (2014) 173 – 177
Daily weight gain was calculated by: Daily weight gain (g/head/day) =Final body weight gain (g) – initial body weight gain (g) During the research (days) Body weight was calculated by weighing the cattle body weight every 1 weeks during the maintenance 3. Results and Discussion Physical form of wafer of feed supplement was a cube with the size of 5x5x5 cm3. The texture ofwafer feed wasrough with the size of coarse particle. The nutrient content of wafer of feed supplement (% Dry Mater) are presented on Table 1. Table 1. Nutrient Content of Wafer of Feed Supplement (% Dry Mater) Wafer of Feed Supplement
Ash (%)
Crude protein (%)
Crude Fiber (%)
Crude fat (%)
NFE (cal/gr)
T1
7.24
32.34
16.85
4.52
39.06
T2
7.91
29.85
16.52
4.69
41.14
T3
6.24
31.24
14.98
3.89
43.64
T4
6.12
31.48
15.26
3.56
43.58
T5
6.49
31.19
17.27
3.63
41.41
Wafer containing lamtoro leaf (T1), wafer containing lamtoro and papaya leaf (T2), wafer containing moringa leaf (T3), wafer containing gamal leaf (T4), wafer containing corn leaf and corn (T5). Wafer of feed supplement hada highcrude protein content. The average crude protein content of wafer of feed supplement was around 29.85-32.34%. Wafer containing lamtoro leaf had the best crude protein content (T1) of 32,34%. Digestibility test on wafer of feed supplement are presented on Table 2. Table 2. Digestibility of Wafer of Feed Supplement Perlakuan
Organicmatter digestibility (%)
T1
Dry matter digestibility (% ) 82.87 ±1.04
NH3
VFA
81.78 ±0.97
9.33 ±0.34
164.55 ±0.00
T2
81.70 ±1.13
81.33 ±1.22
7,63 ±0,00
140.55 ±0.00
T3
76.71 ±1.88
75.67 ±2.57
5,24 ±0,16
102.93 ±16.17
T4
79.36 ± 1.47
78.76±2.47
6,44 ±0,17
126.59 ±16.27
T5
80.41 ±0.19
80.03 ±0.22
7,19 ±0,16
123.29 ±15.85
Wafer containinglamtoro leaf (T1), wafer containing lamtoro and papaya leaf (T2), wafer containing moringa leaf (T3), wafer containing gamal leaf (T4), wafer containing corn leaf and corn (T5). Wafer containinglamtoro leaf had the best digestibility i.e dry matter digestibility of 82.87%, organic matter digestibility of 81.78%, 9.33 NH3 and 164.55 VFA. The results of the first steps research showed that wafer containing lamtoro leaf has the higest nutrient content and digestibility.
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Y. Retnani et al. / APCBEE Procedia 8 (2014) 173 – 177
The second step of the research was feeding by wafer containing lamtoro leaf to stimulate the productivity of Bali calves. The result showed that wafer feeding treatment was significant (P<0.05) on daily weight gain of Bali calves. The feeding treatment did not have significant effect (P>0.05) in blocking the daily weight gain. It means that, wafer of feed supplement given to Bali calves that had the small, medium and big weight had the same response to the wafer of feed supplement. The daily weight gain of Bali calves are presented on Table 3. Table 3. Daily Weight Gain of Bali calves by feeding wafer of feed Supplement (g/head/day) Treatment
Block
Average
B1
B2
B3
R1
33.33
116.67
200.00
R2
50.00
216.67
233.33
R3
350.00
433.33
350.00
116.67 ± 83.33a 166.67 ± 101.38b 377.78 ± 48.11c
c R4 316.67 366.67 450.00 377.78 ± 67.36 R1 (100% of conventional feed), R2 (5% wafer of feed supplement), R3 (10% wafer of feed supplement), R4 (15% wafer of feed supplement). B1 (Small body weight block), B2 (medium body weight block), B3 (Big body weight)
Feeding of 10% and 15% wafer of feed supplement had thesamedaily weight gain (377.78 g/head/day). It suggested that feeding of 10% wafer of feed supplement is optimal. The dailyweight gainin this study is ranged from166.67-377.78g/head/day. The treatments of R3 and R4(10% and 15% of wafer of feed supplement)were higher daily weigth gain thanother treatments. The daily weight gain Bali calves was about 310 g/head/day [6]. According to NRC[7],the daily weight gain was influenced by several factors, i.e. the total consumption of protein, sex, age, genetic, environmental, physiological condition of livestock and management. The result showed thatwafer containing lamtoro leaf treatment was not significant (P>0.05) on body weight of Bali calves during 4 weeks treatment and also did not have significant effect(P>0.05) in blocking body weight of Bali calves. Fig. 1 shows that the average body weight of Bali calves fed by 15% of feed wafer of feed containing lamtoro had the higher average body weight per weeks highest than the other treatment. The Bali calves had the high the responds to the wafer containing lamtoro leaf.
Fig. 1. The Average Body Weight of TheBali Calves.
4. Conclusion It was concluded that bali calves were fed by wafer of feed supplement with level 10% had 69% higher
Y. Retnani et al. / APCBEE Procedia 8 (2014) 173 – 177
than conventional.
References [1] Sasongko WR, Farida SM. Scrutinize Cattle Trade Situation in NTB. BPTP Nusa Tenggara Barat 2012;(http://ntb.litbang.deptan.go.id/ind/index.php?option=com_content&view=article&id=761:menyimak-situasi-perdagangan-sapi-dintb&catid=53:artikel&Itemid=49). [2] Retnani Y, Idat GP, Lia CP. Physical Characteristic and Palatability of Biscuit-Biosupplement For Dairy Goat. Pakistan Journal Of Biological Sciences 2013a; p: 1-5. [3] Retnani Y, Andi S, Taryati. Vegetable Waste as Wafer Feed For Increasing Productivity of Sheep. Asian Jurnal of Animal Sciences 2013b; p: 1-5 [4] Retnani, Y., F.P. Syananta, L. Herawati, W. Widiarti and A. Saenab. Physical Characteristic and Palatability of Market Vegetable Waste Wafer for Sheep. Journal Animal Production 2010a; 12; p. 29 -33. [5] Steel RGD, JH. Torrie. Principles and Procedures of Statistic, 2nd ed. Graw-Hall, Book Comp, New York; 1993. [6] Batubara A, Agussalim..Bioplus effect of bali Cattle. Library of Departement Agriculture 2000; (http://www.pustaka.litbang.deptan.go.id/bptpi/lengkap/IPTANA/fullteks/BPTPsumut/2006B1/pros67.pdf); p:496-501. [7] NRC. Nutrient Requirement of Sheep. 6th Edn. National Academy Press. Washington DC; 1985
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